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This paper aims at understanding the main processes responsible for the erosion/deposition pattern observed on the surface of the Toroidal Pumped Limiter of Tore Supra, using the 3D local impurity transport code ERO. The influence of the plasma impurity content, CX-flux and surface temperature on the global carbon balance and erosion/deposition pattern is discussed. Main results are (1) that considering medium-range transport of C ions is mandatory for reproducing the main characteristics of the global C balance and erosion/deposition pattern, (2) that impurities and CX-atoms increase the erosion by a factor ⩽2 (without changing the net/gross erosion ratio), and (3) that chemical erosion is governed by the re-erosion of deposits, which depends strongly on the surface temperature. [ABSTRACT FROM AUTHOR]

Abstract: Deposited layers in Tore Supra are graphitic disordered carbons and contain spherical nanoparticles, proving the existence of homogeneous growth within the plasma edge, in an unexpected state of advancement. Evidence of homogeneous catalysis comes from the observation of graphite-encapsulated metal particles. Here, carbon particle properties such as temperature and ablation rate in tokamak plasmas are modeled with the DUSTT code, showing that growth can occur in the far scrape-off-layer during normal operation of Tore Supra. These particles can be generated either through plasma chemistry, thanks to efficient trapping in the scrape-off-layer due to sheath repulsion, or through arcing, thanks to transient optimal conditions for catalysis. Their observation on the neutralizer surfaces shows that they are then transported, avoiding destruction. [Copyright &y& Elsevier]

Abstract: This paper presents an analysis of the carbon–deuterium circulation and the resulting balance in Tore Supra over the period 2002–2007. Carbon balance combines the estimation of carbon gross erosion from spectroscopy, net erosion and deposition using confocal microscopy, lock-in thermography and SEM, and a measure of the amount of deposits collected in the vacuum chamber. Fuel retention is determined from post-mortem (PM) analyses and gas balance (GB) measurements. Special attention was paid to the deuterium outgassed during the nights and weekends of the experimental campaign (vessel under vacuum, Plasma Facing Components at 120°C) and during vents (vessel at atmospheric pressure, PFCs at room temperature). It is shown that this outgassing is the main process reconciling the PM and GB estimations of fuel retention, closing the coupled carbon–deuterium balance. In particular, it explains why the deuterium concentration in deposits decreases with increasing depth. [Copyright &y& Elsevier]

Abstract: In order to benchmark predictions for the in vessel tritium inventory in ITER, a survey of fuel retention measured in 4 carbon dominated tokamaks (TEXTOR, ASDEX Upgrade in the 2002–2003 carbon configuration, Tore Supra and JET) was performed, showing retention rates from ∼1g D/h in TEXTOR (L mode, limiter machine) up to ∼6–12g D/h in AUG (H mode, divertor machine). A simple scaling used for ITER predictions is applied for comparison with experimental values: (1) estimate of wall fluxes, (2) estimate of the gross carbon erosion, (3) estimate of the net erosion/redeposition assuming a redeposition fraction and (4) estimate of the retention rate using D/C ratio scalings. The validity of each step is discussed, showing that this approach yields the right order of magnitude, but tends to underestimate the experimental values unless a high wall flux, a low local redeposition fraction and/or a high D/C ratio are used. [Copyright &y& Elsevier]

Abstract: A spatially resolved calculation of the charge exchange particle and energy fluxes on the Toroidal Pumped Limiter (TPL) of Tore Supra is presented, as a first step towards a better understanding and modelling of carbon erosion, migration, as well as deuterium codeposition and bulk diffusion of deuterium in Tore Supra. The results are obtained with the EIRENE code run in a 3D geometry. Physical and chemical erosion maps on the TPL are calculated, and the contribution of neutrals to erosion, especially in the self-shadowed area, is calculated. [Copyright &y& Elsevier]

Abstract: For safety reasons, the formation of carbon deposits in tokamaks must be limited. To understand how these deposits are formed, a comparative study of the characteristics of carbon deposits collected in TEXTOR and Tore Supra tokamaks has been performed. Both deposits exhibit self-similar morphologies like asparagus tips. Transmission electron microscopy performed on thin foils also reveals structure and texture similarities, with the existence of a regular network of parallel mesopores. Besides, methane adsorption isotherm measurements give evidence for microporosity (0.01cm3 g−1 for TEXTOR and 0.06cm3 g−1 for Tore Supra). Raman microspectrometry as well as temperature programmed desorption experiments demonstrate the presence of polyaromatic species, at the origin of the disordered graphitic nature of these carbons. The analysis of samples heat-treated at 2500°C indicates that they graphitize only to a limited extent due to the existence of nanoparticles. Metallic and ferromagnetic inclusions are also evident inside the deposits. These results therefore suggest complex growth processes, mixing homogeneous nucleation and vapor deposition, similar to what can be observed for catalytic chemical vapor deposition processes. [Copyright &y& Elsevier]

Abstract: The sputtering of inside wall components of tokamaks can lead to the injection of supersaturated vapor in the edge plasmas. The resulting condensation favors the formation of clusters which can give rise to solid particulates by further accretion. Sputtering discharges are proposed to have highlight on the formation of carbonaceous dust observed in the tokamaks with graphite based wall components. The flux of the sputtered carbon atoms is evaluated in the conditions of our laboratory discharges as well as the evolution of their energy distribution. It is shown that a cooling mechanism occurs through collisions with the discharge argon atoms, leading to a nucleation phase. A comparison between the carbon structure of the resulting dust particles and a dust sample collected in the Tore Supra tokamak is proposed. The structural differences are discussed and can be correlated to specific plasma conditions. [Copyright &y& Elsevier]

Abstract: Scanning and transmission electron microscopy analyses have been performed for tiles extracted from the toroidal pump limiter of Tore Supra for erosion- and deposition-dominated zones. Deposit thicknesses have been estimated for the plasma-facing top and the gap side lateral surfaces. Deposit thickness profiles have been measured inside gaps, showing that deposition mainly occurs in the first millimetre and that both poloidal and toroidal gap deposition is asymmetric. Quantitative information on the deposit volume and on D-retention are thus obtained from these measurements. Carbon probed at the tile top surfaces is mainly amorphous carbon, due either to the amorphization induced by ion bombardment in the erosion dominated zone, or to deposit formation processes in the deposition-dominated zones. Deposits are tip-shaped and are oriented, which should give information on transport processes. [Copyright &y& Elsevier]

Abstract: The scaling law for carbon erosion in Tore Supra previously established by Hogan et al. (ΦC (C/s)=5×1020 P cond (MW), where P cond is the conducted power) is revisited both from the experimental and the modelling point of view. New developments with the EIRENE code, that allow relating measured CII emission intensities to the total amount of carbon sputtered from the Toroidal Pumped Limiter, are presented. Recent measurements carried out at high input power show a good agreement with the database used to establish the scaling law. [Copyright &y& Elsevier]